From a distance, God’s wrath looks unfair. Why should people be punished for just not believing in Him? But this wrath, and the seven-plague judgement that goes with it, is for more than that. (The plagues could be literal or metaphorical, but that’s beside the point here.)
The picture of heaven being filled with people in white robes playing harps isn’t too far from what John saw:
Revelation 14:2 I saw before me what seemed to be a glass sea mixed with fire. And on it stood all the people who had been victorious over the beast and his statue and the number representing his name. They were all holding harps that God had given them.
Everyone gets a white robe—it’s the righteousness of Jesus. Everyone worships God, and some of us, those who refuse to worship the beast or take that mark, get to play harps. That’ll mean a miraculous and sudden musical ability for some of us, but it’s heaven, so miraculous things are quite likely.